After using Chomp SMS for quite some time I became frustrated with the idea that if I sent a delayed text message but had my phone in airplane mode or if it was off the text would not be sent until after the time I had specified.
To solve this I began using Boomerang in conjunction with Google Voice to send messages at exactly the right time regardless of the status of my phone.
The idea is that when you use Google Voice to send an sms message it generates an email account that bridges your phone number and that of the recipient. In order to create this address send a message and upon getting a reply the Gmail account that is connected to Google Voice will now show the conversation as an email.
https://vimeo.com/28478253
It's a relief to have extra protection from spam and a throwaway phone number to give people you don't know. You can edit Google Voice settings to forward texts to your phone so that all your texts wind up in your normal texting app.
Try it out. All you have to do is schedule an email to be sent via the Boomerang app and then turn off your phone. After the text has been sent check Google Voice. You will see that it has in fact been sent at the correct time as Boomerang prompts Gmail to do so and the email registers itself as a Google Voice conversation.
And did I mention that both apps are free?
http://www.boomerangapp.com/
https://voice.google.com/about
